Feeder assembly for particle blast system

ABSTRACT

A particle blast system includes a feeder assembly having a rotor with a plurality of pockets formed in the peripheral surface. The transport gas flowpath includes the pockets, such that substantially all transport gas flows through the pockets. The seal adjacent the peripheral surface is actuated by the transport gas pressure to urge its sealing surface against the rotor&#39;s peripheral surface. At start up, there is no substantial pressure between the seal and the rotor, reducing start up torque requirements.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to particle blastsystems, and is particularly directed to a device which providesimproved introduction of particles into a transport gas flow forultimate delivery as entrained particles to a workpiece or other target.The invention will be specifically disclosed in connection with atransport mechanism in a cryogenic particle blast system whichintroduces particles from a source of such particles, such as a hopper,into the transport gas flow.

[0002] Particle blasting systems have been around for several decades.Typically, particles, also known as blast media, are fed into atransport gas flow and are transported as entrained particles to a blastnozzle, from which the particles exit, being directed toward a workpieceor other target.

[0003] Carbon dioxide blasting systems are well known, and along withvarious associated component parts, are shown in U.S. Pat. Nos.4,744,181, 4,843,770, 4,947,592, 5,050,805, 5,018,667, 5,109,636,5,188,151, 5,301,509, 5,571,335, 5,301,509, 5,473,903, 5,660,580 and5,795,214, and in commonly owned co-pending applications Ser. No.09/658,359, filed Sept. 8, 2000, titled Improved Hopper and Ser. No.09/369,797, filed Aug. 6, 1999, titled Non-Metallic Particle BlastingNozzle With Static Field Dissipation, all of which are incorporatedherein by reference. Many prior art blasting system, such as disclosedtherein, include rotating rotors with cavities or pockets fortransporting pellets into the transport gas flow. Seals are used incontact with the rotor surface in which the cavities or pockets areformed. Such seals are usually urged against the rotor surfaceindependent of whether the rotor is rotating or the system is operating.The seal force results in seal drag, creating a resisting torque whichhas to be overcome by the motor. When the torque is present at the timethe rotor is started turning, a substantial start up load is placed onthe motor, affecting the size and wear of the motor. The prior art largediameter rotors also provide a sizable moment arm through which the sealdrag produces substantial torque.

[0004] At least for prior art rotors which utilize pockets formed in aperipheral rotor surface, not all pellets are discharged from thepockets at the discharge station. Additionally, the pocket spacing andlack of thorough, uniform mixing of the transport gas and pellets in thefeeder results in pulses.

[0005] Although the present invention will be described herein inconnection with a particle feeder for use with carbon dioxide blasting,it will be understood that the present invention is not limited in useor application to carbon dioxide blasting. The teachings of the presentinvention may be used in application in which there can be compaction oragglomeration of any type of particle blast media.

BRIEF DESCRIPTION OF THE DRAWING

[0006] The accompanying drawings incorporated in and forming a part ofthe specification illustrate several aspects of the present invention,and together with the description serve to explain the principles of theinvention. In the drawings:

[0007]FIG. 1 is a perspective side view of a particle blast systemconstructed in accordance with the teachings of the present invention.

[0008]FIG. 2 is a perspective view of the feeder assembly and motor ofthe particle blast system of FIG. 1.

[0009]FIG. 3 is a perspective view of the feeder assembly of theparticle blast system of FIG. 1, similar to FIG. 2 but without themotor.

[0010]FIG. 4 is a side view of the particle blast system of FIG. 1.

[0011]FIG. 5 is cross-sectional view of the particle blast system takenalong line 5-5 of FIG. 4.

[0012]FIG. 6 is an exploded, perspective view of the feeder assembly.

[0013]FIG. 7 is a side view of the feeder assembly and motor of FIG. 2.

[0014] FIGS. 8A-I are cross-sectional views of the feeder assembly takenalong line 8-8 of FIG. 7, showing the rotor in successive rotationalorientations.

[0015]FIG. 9 is a perspective view of the lower pad of the feederassembly.

[0016]FIG. 10 is a top view of lower pad of FIG. 9.

[0017]FIG. 11 is a bottom view of the lower pad of FIG. 9.

[0018]FIG. 12 is a cross-sectional view of the feeder assembly takenalong line 12-12 of FIG. 7.

[0019]FIG. 13 is a cross-sectional view of the feeder assembly takenalong line 13-13 of FIG. 7.

[0020]FIG. 14 is top view of the feeder assembly.

[0021]FIG. 15 is a is a cross-sectional view of the feeder assemblytaken along line 15-15 of FIG. 14.

[0022]FIG. 16 is a side view of the feeder assembly.

[0023]FIG. 17 is a cross-sectional view of the feeder assembly takenalong line 17-17 of FIG. 16.

[0024]FIG. 18 is a perspective view of a rotor.

[0025]FIG. 19 is a side view of the rotor of FIG. 18.

[0026] Reference will now be made in detail to the present preferredembodiment of the invention, an example of which is illustrated in theaccompanying drawings.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0027] Referring now to the drawings in detail, wherein like numeralsindicate the same elements throughout the views, FIG. 1 shows particleblast system, generally indicated at 2, with the outside cover omittedfor clarity. Particle blast system 2 includes frame 4 which supports thevarious components. Particle blast system 2 includes hopper 6, whichholds the blast media (not shown), functioning as a source of blastmedia. In the embodiment depicted, particle blast system 2 is configuredto use sublimeable particles, particularly carbon dioxide pellets, asthe blast media. It is noted that the present invention may be used witha wide variety of blast media, including non-cryogenic blast media.

[0028] Particle blast system 2 includes feeder assembly 8, also referredto as the feeder, which is driven by motor 10. Feeder 8 includes inlet12 and outlet 14. A transport gas flowpath is formed within feeder 8between inlet 12 and outlet 14 (not seen in FIG. 1) as describedhereinafter. Inlet 12 is connected to a source of transport gas, andoutlet 14 is connected to the delivery hose (not shown) which transportsthe carbon dioxide pellets entrained in the transport gas to the blastnozzle (not shown). As can be seen in FIGS. 1 and 4, conduit 16 isconnected to inlet 12, and includes end 16 a extending outside of frame4 for easy connection to a source of transport gas. FIG. 1 illustratesoutlet 14 as being connected to hose 18, which includes end 18 aextending outside of frame 4 for easy connection to the delivery hose(not shown).

[0029] As is well known, the transport gas may be at any pressure andflow rate suitable for the particular system. The operating pressures,flow rates and component (such as compressor) size are dependant on thecross-section of the system blast nozzle (not shown). The source oftransport gas may be shop air. Typically, despite treatment, thetransport gas will have some humidity left in it. In the depictedembodiment, the transport gas at the rotor had a pressure of about 80PSIG with a nominal flow rate of 150 SCFM, at around room temperature,which matched the particular system blast nozzle used. The operatingpressure for such a system ranges from about 30 PSIG to about 300 PSIG,the upper maximum being dictated by the rating of the components. Themaximum rotor speed was about 70 RPM, at which the system deliveredapproximately 7 pounds of CO₂ pellets per minute.

[0030]FIG. 2 shows feeder assembly 8 connected to motor 10, throughcoupling 20. As can be seen in FIG. 3, from which motor 10 and cover 22have been omitted, coupling 20 is a jaw type coupling formed by theintermeshing of a plurality of legs 24 which extend from an end of rotor26. Complementarily shaped legs are found on motor 10, providing easydisengagement through axial movement between motor 10 and rotor 26.Coupling 20 allows radial and axial misalignment and provides for easydisassembly.

[0031]FIG. 5 illustrates a cross sectional view of hopper 6 and feeder8. As shown, hopper exit 28 is aligned with inlet 30 of feeder 8. Sealassembly 32 seals between exit 28 and feeder 8, sealingly engaging uppersurface 34 a of upper seal pad 34. Ramrod assembly 35 is illustratedextending to the side. Inlet 12 has coupling 12 a threaded thereto.Outlet 14 has coupling 14 a threaded thereto.

[0032]FIG. 6 is an exploded perspective view of feeder 8. Feeder 8includes feeder block 36 in which inlet 12 and outlet 14 are formed.Feeder block 36 includes cavity 38 defined by wall 38 a and bottom 38 b.Feeder block 36 is secured to plate 37 which is secured to base 40 whichis secured to frame 4. A pair of spaced apart bearing supports 42, 44respectively carry axially aligned sealed bearings 46, 48.

[0033] Rotor 26 is made from 6061 hard coat anodized aluminum, and isdepicted as a cylinder, although various other shapes, such asfrustoconical may be used. In the depicted embodiment, rotor 26 has adiameter of two inches. The present invention includes the use of arotor having a diameter of approximately four inches. Threaded hole 26 bis formed in the end of rotor 26 to provide for removal or rotor 26.Rotor 26 includes peripheral surface 50, in which a plurality of spacedapart pockets 52 are formed. In the embodiment shown, there are fourcircumferential rows of pockets 52, with each circumferential row havingsix pockets 52. Pockets 52 are also aligned in axial rows, with eachaxial row having two pockets 52. The axial and circumferential rows arearranged such that the axial and circumferential widths of pockets 52overlap, but do not intersect, each other.

[0034] In this embodiment, rotor 26 is rotatably carried by bearings 46,48, for rotation by motor 10 about rotor axis 26 c. Rotor 26 is retainedin place by motor 10 at end 26 a, with thrust bearing plate 56 andretaining plate 54 retaining rotor 26 at the other end. Thrust bearingplate 56 is made of UHMW plastic. The fit between bearings 46, 48, androtor 26 allows rotor 26 to be easily withdrawn from feeder assembly 8by removing retaining plate 54 and thrust bearing plate 56, and slidingrotor out through bearing 46. A threaded shaft, such as a bolt, may beinserted into hole 26 b to aid in removal of rotor 26.

[0035] In the embodiment depicted, the configuration of feeder 8 doesnot require any axial loading on rotor 26, either from sealing or thebearings. The end play or float of rotor 26 was about 0.050 inches.

[0036] Lower seal pad 58 is disposed partially in cavity 38, with seal60, located in groove 62, sealingly engaging groove 62 and wall 38 a.Lower seal pad 58 includes surface 64 which, when assembled, contactsperipheral surface 50 of rotor 26, forming a seal therewith, asdescribed below. As used herein, “pad” is not used as limiting: “Sealpad” refers to any component which forms a seal.

[0037] Upper seal pad 34 includes surface 66 which, when assembled,contacts peripheral surface 50 of rotor 26. Fasteners 68 engage holes inupper seal pad 34 to hold it in place, without significant force beingexerted by surface 66 on rotor 26. Intermediate seal 70 may be disposedbetween upper seal pad 34 and lower seal pad 58.

[0038] Upper seal pad 34 and lower seal pad 58 are made of a UHMWmaterial. The ends of surfaces 64 and 66 adjacent bearing 46 arechamfered to allow easier insertion of rotor 26.

[0039] Ramrod assembly 35 includes two ramrods 35 a and 35 b which aremoved between a retracted position to a position at which they extendinto entrance 30 of feeder 8. Ramrods 35 a and 35 b are actuated bypneumatic cylinders 33 a and 33 b respectively, which are carried bymounting plate 31. Mounting plate 31 is secured at either end to bearingsupports 42 and 44 by fasteners 27, with spacer 29 disposed adjacentmounting plate 31. Spacer 29 includes openings 29 a and 29 b which alignwith openings 30 a and 30 b in seal 34. Copending application Ser. No.09/658,359 provides a description of the operation of ramrods. Anyfunctional number of ramrods may be used, for example only one or morethan two. They may be oriented differently than as shown in FIG. 6, suchas at 90° to that illustrated, aligned with axis of rotation 26 c. Theymay operate simultaneously, alternating or independently. They may bedisposed at angles to each other.

[0040] FIGS. 8A-I are cross-sectional views of the feeder assembly takenalong line 8-8 of FIG. 7, and show rotor 26 in successive rotationalorientations. FIG. 8A shows lower pad seal 58 disposed in cavity 38,with seal 68 engaging wall 38 a, and upper pad seal 34 overlying lowerpad seal 58. Referring also to FIGS. 9-11, which show various views oflower seal pad 68, upper pad seal 34 is disposed adjacent upper surface58 a of lower pad seal 58. On one side, labyrinth seal 70 is formedbetween upper pad seal 34 and lower pad seal 58 by the cooperation ofstep 58 b with downwardly extending wall or lip 34 c. Thus, lower padseal 58 overlaps with upper pad seal 34 at this stepped joint keepsambient air from entering the hopper. With the stepped design, lower padseal 58 can move vertically independent of upper pad seal 34, allowingsubstantially all force on lower seal pad 58 functions to urge surface64 in sealing contact with surface 50, as described below. On theopposite side, vent 96 is formed, which allows pressurized transport gasto escape from pockets 52 as they pass thereby, as described below. Vent96 is defined by step 34 d formed in upper seal 34 and surface 58 c aportion of which is downwardly inclined. The slight incline of a portionof surface 58 c prevents water from puddling when water ice that maybuild up on the feeder thaws.

[0041] Surface 64 includes two openings 72 which are in fluidcommunication with inlet 12 through upstream chamber 74, and twoopenings 76 which are in fluid communication with outlet 14 throughdownstream chamber 78. It is noted that although two openings 72 and twoopenings 76 are present in the illustrated embodiment, the number ofopenings 72 and openings 76 may vary, depending on the design of feeder8. For example, a single opening may be used for each. Additionally,more than two openings may be used for each.

[0042] Feeder 8 has a transport gas flowpath from inlet 12 to outlet 14.In the depicted embodiment, passageways 80 and 82 are formed in feederblock 36. Lower seal pad 58 includes recess 84, which is aligned withinlet 12 and together with passageway 80, places upstream chamber 74 influid communication with inlet 12. Lower seal pad also includes recess86, which is aligned with outlet 14 and together with passageway 82,places downstream chamber 78 in fluid communication with outlet 14.

[0043] Upstream chamber 74 is separated from downstream chamber 76 bywall 88 which extends transversely across lower seal pad 58, in the samedirection as axis of rotation 26 c. Lower surface 88 a of wall 88 sealsagainst bottom 38 b of cavity 38, keeping upstream chamber 74 separatefrom downstream chamber 78. Wall 90 is disposed perpendicular to wall88, with lower surface 90 a engaging bottom 38 b.

[0044] As illustrated, in the depicted embodiment, inlet 12 is in fluidcommunication with outlet 14 only through individual pockets 52 as theyare cyclically disposed by rotation of rotor 26 between a first positionat an individual pocket first spans openings 72 and 76 and a secondposition at which the individual pocket last spans openings 72 and 76.This configuration directs all of the transport gas entering inlet 12 topass through pockets 52, which pushes the blast media out of pockets 52,to become entrained in the transport gas flow. Turbulent flow occurs indownstream chamber 78, promoting mixing of media with the transport gas.Such mixing of the media minimizes entrains the media in the transportgas, minimizing impacts between the media and the feeder componentsdownstream of the pockets. This means that the particles are onlysignificantly in contact with the rotor, minimizing heat transfer to theparticles from other components of feeder 8. The significant flow of thetransport gas through each pocket 52 acts to effectively clean all mediafrom each pocket 52.

[0045] For cryogenic particles, this transport gas flowpath, in whichall or substantially all flows through pockets 52, aids in the transferof heat from the transport gas to rotor 26, which helps reduce orprevent water ice (which forms due to humidity in the transport gas)from freezing on the rotor and other parts of feeder 8. Heat transferbetween rotor 26 and non-moving components of feeder 8 is minimized byuse of the UHMW pad seals surrounding rotor 26. Substantially all heatgain or loss of the rotor is from the particles and transport gas. Thesmall mass of rotor 26 makes it easier for the transport gas to heatrotor 26. Additionally, rotor 26 could carry a heater element, orpassageways could be provided for the flow of heated air primarily forheating rotor 26. Such passages could be in rotor 26. Of course, thenecessary rotational coupling for such heater element or passagewayswould have to be provided.

[0046] Although the depicted embodiment is configured to direct all thetransport gas through the pockets, is possible to configure a particleblast system to utilize this aspect of the present invention, butwithout directing all transport gas through the pockets, such as bybypassing a portion of the transport gas flow around the feeder, or evenbypassing a portion of the transport gas flow around the pocket. Thepresent invention is applicable to such particle blast systems.

[0047] FIGS. 8A-I illustrate the progress of pocket 52 a past openings76 and 72 as rotor 26 is rotated. In the depicted embodiment, rotor 26rotates clockwise, presenting pockets 52 in an endless succession firstpast openings 76 and then openings 72 in a periodic, cyclical nature. Itis noted that alternatively, rotor 26 could rotate in the oppositiondirection, exposing pockets first to openings 72 and then openings 76.Pockets 52 are filled with blast media, in particular in this embodimentcarbon dioxide pellets, from hopper 6 through opening 92 in upper sealpad 34. The action of the small radius (e.g., in the depictedembodiment, four inches or less) of rotor 26 past opening edge 92 atends to bite into any agglomerated chunks of pellets, breaking themapart, reducing blockage and promoting more complete fill.

[0048] In FIG. 8A, leading edge 52 b of pocket 52 a is illustratedlocated about midway in opening 76. Once leading edge 52 b has traveledpast edge 76 a of opening 76 a sufficient distance, pellets will beginto exit pocket 52 a.

[0049]FIG. 8B illustrates leading edge 52 b just reaching edge 76 b ofopening 76. At this position, the entire circumferential width ofopening 76 is exposed to pocket 52 a, it being noted that as a result ofthe roughly circular shape of the opening of pocket 52 a, thecross-sectional area of the opening of pocket 52 a exposed to opening 76(as well as opening 72) varies with the angular position of pocket 52 a.

[0050] At the position illustrated in FIG. 8B, transport gas cannot flowfrom inlet 12 to outlet 14 through pocket 52 a, being blocked by sealingengagement between rotor 26 and edge 88 b of wall 88. Because in theembodiment depicted, openings 72 and 76 are always spanned by at leasttwo pockets 52, inlet 12 is always in fluid communication with outlet14, but only through pockets 52.

[0051] Alternatively, the level of edge 88 b could be reduced, creatinga gap such that a complete seal with rotor 26 is not formed by wall 88,providing a continuous flowpath from inlet 12 to outlet 14 from thefirst passageway, defined by lower pad seal 58 which is in fluidcommunication with opening 72 to the second passageway, defined by lowerpad seal 58 which is in fluid communication with opening 76, through thepassageway defined by edge 88 b of wall 88 and the peripheral surface 50of rotor 26, not through pockets 52. Such a continuous flow path wouldreduce pulsing as the size of the flow path cyclically varies with therotation of rotor 26. Of course, in such an embodiment, as pockets 52are moved between the first and second positions, there is a substantialincrease in the flowpath area, and a substantial volume of transport gasflows through the aligned pockets 52.

[0052]FIG. 8C illustrates leading edge 52 b of pocket 52 a at a firstposition just reaching edge 72 a of opening 72, whereat pocket 52 afirst begins spanning opening 76 and 72. FIG. 8D illustrates rotor 26rotated slightly further, with leading edge 52 b just past edge 72 a.Once leading edge 52 b passes edge 76 a, there is a continuous transportgas flowpath from opening 72 to opening 76 through pocket 52 a. At theposition shown in FIG. 8D, transport gas will flow from upstream chamber74, through opening 72, pocket 52 a and opening 76 a, to downstreamchamber 76, as indicated by arrow 94.

[0053] The transport gas pushes pellets from pocket 52 a out opening 76,into downstream chamber 78 where mixing of the pellets and transport gasoccurs, and pellets exit feeder 8 through outlet 14, entrained in thetransport gas.

[0054]FIG. 8E illustrates leading edge 52 b when it first reaches edge72 b. FIG. 8F shows leading edge 52 b well past edge 72 b, with trailingedge 52 c approaching edge 76 b at which the flowpath through pocket 52a will stop, the position at which pocket 52 a is no longer part of thetransport gas flowpath (until the next cycle).

[0055]FIG. 8G shows trailing edge 52 c past edge 76 b, at edge 72 a. Ascan be seen, pocket 52 a is no longer exposed to downstream chamber 78,but is exposed to pressurized transport gas. FIG. 8H illustratestrailing edge 52 c past edge 72 b, with pressurized transport gastrapped therein.

[0056]FIG. 8I illustrates pocket 52 a rotated further, aligned with vent96, which allows the pressurized transport gas that was trapped withinpocket 52 a to escape.

[0057] As previously mentioned, upper seal pad is held in engagementwith rotor 26 by fasteners 68 without significant force being exerted bysurface 66 on rotor 26. Ambient pressure is present within hopper 6.Upper seal pad 34 functions not only in the filling of pockets 52, butalso to keep ambient moisture from entering the system through feeder 8.Adequate sealing is achieved between surface 66 and surface 50 withoutany significant force urging upper seal pad 34 toward rotor 26.

[0058] The seal between rotor surface 50 and lower seal pad surface 64is very important. The pressurized transport gas must be contained, bothfor efficiency of the delivery of pellets to the blast nozzle andbecause leakage into the low pressure side of rotor 26 and into hopper 6will cause agglomeration and other deleterious effects. The presentinvention utilizes the pressure of the transport gas to providesubstantially all the sealing force between rotor surface 50 and sealsurface 64.

[0059] When pressurized transport gas is not present (in the depictedembodiment, when transport gas is not flowing through the transport gasflowpath), there is no substantial force between rotor surface 50 andsurface 64. When rotation of rotor 26 is started at the same orapproximately the same time as transport gas is allowed to begin to flow(such as occurs in many particle blast systems when the blast trigger isdepressed), there is no substantial force on rotor surface 50. Thismeans that motor 10 does not have to be sized to start under load, whichreduces the horsepower requirements, allowing a smaller, less expensivemotor to be used. Rotor 26 will be very close to its steady state speedby the time the transport gas pressure results in substantial sealingforce on rotor surface 50.

[0060] Referring to FIG. 81 for clarity of explanation, as describedabove, lower seal pad 58 is disposed partially in cavity 38, with seal68 sealing between wall 38 a and lower seal pad 58. Surface 98 is spacedapart from surface 64, and together they define arcuate wall 100.Although walls 88 and 90 extend from arcuate wall 100, arcuate wall 100is a relatively thin wall which is sufficiently flexible to transmit asubstantial portion of pressure exerted against surface 98 to rotorsurface 50 by surface 64. Surface 98 a of surface 98 defines a portionof upstream chamber 74. When transport gas is flowing through thetransport gas flowpath, the pressure of the transport gas withinupstream chamber 74 bears on surface 98 a, urging the overlying portionsurface 64 a of surface 64 against rotor surface 50. The flexibility ofarcuate wall 100 a allows arcuate wall to conform to the shape of rotorsurface 50, and transmit a substantial portion of the pressure tosurface 64 a, urging surface 64 a into sealing contact with rotorsurface 50.

[0061] Similarly, surface 98 b of surface 98 defines a portion ofdownstream chamber 76. When transport gas is flowing through thetransport gas flowpath, the pressure of the transport gas withindownstream chamber 76 bears on surface 98 b, urging the overlyingportion surface 64 b of surface 64 against rotor surface 50. Theflexibility of arcuate wall 100 b allows arcuate wall to conform to theshape of rotor surface 50, and transmit a substantial portion of thepressure to surface 64 b, urging surface 64 b into sealing contact withrotor surface 50.

[0062] In the illustrated embodiment, seal surface 64 contacts rotorsurface 50 over an angle of about 180°. The depicted configurationallows the sealing force to be exerted throughout substantially theentire contact angle, and substantially normal to rotor surface 50. Ofcourse other seal arrangements, even those that are not activated by gaspressure, may also be used with the pockets being part of thetransportation gas flowpath.

[0063] It is noted that as the pressure of the transport gas increases,the required sealing force between rotor surface 50 and surface 64increases. In the depicted embodiment, the sealing force between rotorsurface 50 and surface 64 is proportional to the transport gas pressure.In turn, the load on rotor 26 and motor 10 is proportional to thetransport gas pressure. This reduces rotor and seal wear, and increasesmotor life.

[0064] Although in the depicted embodiment it is the gas pressure of thetransport gas within the transport gas flowpath which urges surface 64against rotor surface 50, the pressure which actuates the seal againstrotor surface 50 may come from any source. For example, inner surface 98may be exposed to pressurized transport gas by a chamber or passagewayconnected to but not within the direct transport gas flowpath. Thepressure of the gas within such a chamber or passageway may becontrolled separate from the pressure of the transport gas. The chambermay be not connected to the transport gas flowpath, with a separatesource of fluid pressure being used to urge surface 64 into sealingengagement with rotor surface 50.

[0065] Configurations other than as depicted in the illustratedembodiment may be used to provide the sealing force. For example, aplurality of internal passageways may be formed adjacent surface 64which urge surface 64 into sealing engagement with rotor surface 50 whenpressure is present in such internal passageways. It is noted that thedynamic pneumatically actuated seal unloads rotor 26 when not inoperation, make rotor removal easier than designs that require seals beunloaded before rotor removal.

[0066] It is noted that only one circumferential row of pockets 52 isvisible in FIGS. 8A-I. In the depicted embodiment, there is anadditional circumferential row of pockets 52 which is axially alignedwith the depicted row, and two other circumferential rows of pockets 52which aligned with each other but staggered with respect to the othertwo aligned circumferential rows. Thus, in the depicted embodiment,there are always at least two pockets 52 exposed to both openings 72 and76, allowing the transport gas to flow continuously from upstreamchamber 74 to downstream chamber 76. The arrangement of pockets 52 inthe depicted embodiment thus keeps inlet 12 in continuous fluidcommunication with outlet 14. The depicted configuration, including thearrangement of pockets 52, the flow through pocket, and downstreammixing chamber 78, functions to reduce pulsing of blast media.

[0067] The shape and depth of pockets 52 may vary. Obviously, sufficientwall thickness must remain between pockets 52 to maintain structuralintegrity and sufficient sealing at surface 50. Different pocket openingshapes may be used. It is noted that openings with leading edges thatare parallel to edges 72 a, 72 b, 76 a and 76 b, and/or too much axialwidth can allow deflection in surfaces 64, as well as 66, resulting inthe pocket opening gouging those surfaces. In the depicted embodiment,the volume of pockets 52 was as large as possible, given the physicalconstraints, so as to maximize the volume for receiving and transportingpellets. In the depicted embodiment, laminar flow does not occur throughpockets 5, promoting better removal of pellets as the transport gasflows therethrough.

[0068] The size and number of pockets 52, as well as rotational speed ofrotor 26, determine how much blast media can be introduced into thetransport gas flow and ultimately how much blast media can be directedtoward a target from the blast nozzle. Rotor 26 is substantially smallerin diameter than other radial transport rotors, being in the depictedembodiment about two inches in diameter. The smaller diameter results inless torque developed by the seal pressure. This, in addition to thelack of significant seal drag at start up, allows a smaller motor to beused. The small diameter rotor also has a lower moment of inertia, whichalso reduces the power required for rotation. In contrast, prior artmotors were at least one horsepower. In the depicted embodiment, for thesame pellet delivery rate, motor 10 is can be a half or quarterhorsepower motor, perhaps even lower. This lower torque requirementallows, if desired, the use of a pneumatic motor.

[0069] The rotational speed of rotor 26 in the depicted embodiment is 70RPM, compared to 20 RPM of similar prior art large diameter rotors. Forthe depicted arrangement of pockets 52, this speed results in the samerate of pocket exposure at the discharge station as the slower moving,larger diameter rotors of the prior art. If the large diameter prior artrotors rotated too fast, the pockets would not fill, similar tocavitation resulting from the characteristics of the pellets, meaningthat rotating the rotor above a certain speed would not increase thepellet delivery rate. However, the small diameter rotor, one aspect ofthe present invention, is able to fill properly even when rotated at thehigher rotational speed.

[0070] By keeping the rate of pocket exposure, based on diameter,rotational speed and pocket opening, at approximately the same as largerprior art rotors, the smaller diameter rotor is used as describedherein. The volume of pocket exposure is also important. The smallerrotor dictates deeper pockets and more pockets to obtain the samevolume. Filling the deeper pockets requires more time than shallowpockets of the same volume, thereby affecting rotational speed. Forexample, in one embodiment, a 14% deeper pocket depth was combined witha 14% drop in rotational speed of the small rotor of the equivalentsmall rotor rate of pocket exposure.

[0071] Additional benefit is obtained by the increased speed, reducingthe time that pellets spend in a given pocket, thereby reducing the timethat the pellets can cool the rotor. In the configuration shown, withoppositely aligned charge and discharge stations, pellets are in a rotorpocket for approximately half of each rotation. The “dwell” time forpellets in a pocket are the same for the same rate of pocket exposure,regardless of rotor diameter. However, the small diameter rotor reducesthe total variation in temperature by reducing cycle time.

[0072] Different ranges of delivery rates may be achieved by providing avariety of rotors having different pocket arrangements, such as pocketsof different sizes or a different number of pockets. The rotorrotational speed can then be varied to control the exact delivery ratewithin the range. However, the control system may provide only a singlerotor speed. Rotors may be easily changed by removal of retaining plate54, as discussed above.

[0073] Referring to FIG. 12, there is shown a cross-sectional view takenalong line 12-12 of FIG. 7, showing a section through lower seal pad 58.FIG. 13 is a cross-sectional view taken along line 13-13 of FIG. 7,showing a section through lower seal pad 58 at a location closer tobottom 38 b of feeder block 36. Passageways 80 and 82 can be seen,formed in bottom 38 b.

[0074]FIG. 14 is a top view of feeder 8, with plurality of pockets 52 ofrotor 26 clearly visible through opening 92. Inclined surfaces 92 b and92 c allow opening to be larger than the opening 92 adjacent rotor 26.It is noted that the width (as taken parallel to section line 15-15) ofopening 92 is larger than similar prior art feeders, with the ratio oflength to diameter of rotor 26 being substantially larger than that ofprior art feeders.

[0075]FIG. 15 is a cross-sectional view taken along line 15-15 of FIG.14. Section line 15-15 cuts through downstream chamber 78 so that wall88 is seen in fall view and wall 90 is seen in section view.

[0076]FIG. 16 is a side view of feeder 8, and FIG. 17 is across-sectional view taken along line 17-17 of FIG. 16. FIGS. 15 and 17are similar in that the section is taken through the center of rotor 26.However, in FIG. 17, the lower portion of the section is taken closer tooutlet 14, showing surface 78 a of downstream chamber 78 and wall 90 infull view.

[0077] Any suitable shape for pockets 52 may be used. FIGS. 18 and 19provide further illustration of pockets 52 of the rotor depicted herein.The mouth of the pockets, at surface 50 of rotor 26, have been enlargedrelative to the rest of the pocket. Due to the cylindrical shape ofrotor 26, the wall thickness between adjacent pockets 52 is smallercloser to the rotor's center. In contrast, at surface 50, the pocketcenters are further apart, allowing the pocket openings to be larger. Itis noted that in the depicted embodiment the outside edges 52 d ofeither outer circumferential row of pockets 52 are not the same shape asthe pocket openings of the inner two circumferential rows. This matchesexisting hopper throat size, but it will be recognized that such anopening configuration is a limitation.

[0078] The present invention allows the utilization of a rotor having adiameter to width (sealing width) of below 1:1, such as in the depictedembodiment 1:2. Prior art rotors operating at pressures in the range of30-300 PSIG, such as is typically found with cryogenic particleblasting, are known to fall around 8:1.25.

[0079] The foregoing description of an embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Obvious modifications or variations are possible in light ofthe above teachings. The embodiment was chosen and described in order toillustrate the principles of the invention and its practical applicationto thereby enable one of ordinary skill in the art to best utilize theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto.

What is claimed is:
 1. A feeder configured to transport blast media froma source into a flow of transport gas, said feeder comprising: a) arotor having a peripheral surface, said rotor being rotatable about anaxis of rotation; b) a plurality of pockets disposed in said peripheralsurface, each of said plurality of pockets being cyclically disposedbetween a first position and a second position when said rotor isrotated about said axis; c) a transport gas flowpath, said transport gasflowpath having an inlet and an outlet, said inlet being configured tobe connected to a source of transport gas; d) a seal having a firstsurface contacting at least a portion of said peripheral surface, saidfirst surface having at least one first opening and at least one secondopening spaced apart from each other, said at least one first openingbeing in fluid communication with said inlet, said at least one secondopening being in fluid communication with said outlet; and e) saidtransport gas being able to flow from said at least one first opening tosaid at least one second opening through those of said plurality ofpockets disposed between said first and second positions.
 2. The feederof claim 1, wherein said seal includes a downstream chamber, said atleast one second opening being in fluid communication with said outletthrough said downstream chamber.
 3. The feeder of claim 2, wherein awall is defined by said first surface and a second, spaced apartsurface, said wall being sufficiently flexible to transmit a substantialportion of pressure exerted against said second surface by transport gaspresent within said downstream chamber to said peripheral surface bysaid first surface when transport gas is flowing through said transportgas flowpath.
 4. The feeder of claim 1, wherein said seal includes anupstream chamber, said at least one first opening being in fluidcommunication with said inlet through said upstream chamber.
 5. Thefeeder of claim 4, wherein a wall is defined by said first surface and asecond, spaced apart surface, said wall being sufficiently flexible totransmit a substantial portion of pressure exerted against said secondsurface by transport gas present within said upstream chamber to saidperipheral surface by said first surface when transport gas is flowingthrough said transport gas flowpath.
 6. The feeder of claim 1, whereinthere is no substantial force between said peripheral surface and saidfirst surface when transport gas is not flowing through said transportgas flowpath.
 7. The feeder of claim 1, wherein said first surface isurged into sealing contact with said peripheral surface when transportgas is flowing through said transport gas flowpath.
 8. The feeder ofclaim 7, wherein substantially all sealing force between said firstsurface and said peripheral surface is created by said transport gasflowing through said transport gas flowpath.
 9. The feeder of claim 1,wherein a wall is defined by said first surface and a second spacedapart surface, said wall being sufficiently flexible to transmit asubstantial portion of pressure exerted against said second surface bytransport gas to said peripheral surface by said first surface whentransport gas is flowing through said transport gas flowpath.
 10. Thefeeder of claim 1, wherein said transport gas is able to flow from saidat least one first opening to said at least one second opening onlythrough those of said plurality of pockets disposed between said firstand second positions.
 11. The feeder of claim 1, wherein a portion ofsaid transport gas does not flow through said first and second openings.12. The feeder of claim 1, comprising a passageway defined at leastpartially by said seal, a portion of transport gas being able to flowfrom said at least one first opening to said at least one second openingthrough said first passageway.
 13. The feeder of claim 1, wherein saidplurality of pockets are arranged such that said transport gas is ableto flow continuously from said at least one first opening to said atleast one second opening when said rotor is rotated.
 14. The feeder ofclaim 1, wherein said wall contacts said peripheral surface over anangle of about 180°.
 15. The feeder of claim 1, wherein said seal is ofunitary construction.
 16. A particle blast system comprising: a) asource of blast media; b) a discharge nozzle for expelling blast mediafrom said system; and c) a feeder configured to transport blast mediafrom said source into a flow of transport gas, said feeder assemblycomprising: i) a rotor having a peripheral surface, said rotor beingrotatable about an axis of rotation; ii) a plurality of pockets disposedin said peripheral surface, each of said plurality of pockets beingcyclically disposed between a first position and a second position whensaid rotor is rotated about said axis; iii) a transport gas flowpath,said transport gas flowpath having an inlet and an outlet, said inletbeing configured to be connected to a source of transport gas; iv) aseal having a first surface contacting at least a portion of saidperipheral surface, said first surface having at least one first openingand at least one second opening spaced apart from each other, said atleast one first opening being in fluid communication with said inlet,said at least one second opening being in fluid communication with saidoutlet; and v) said transport gas being able to flow from said at leastone first opening to said at least one second opening through those ofsaid plurality of pockets disposed between said first and secondpositions.
 17. The particle blast system of claim 16, wherein said sealincludes a downstream chamber, said at least one second opening being influid communication with said outlet through said downstream chamber.18. The particle blast system of claim 17, wherein a wall is defined bysaid first surface and a second, spaced apart surface, said wall beingsufficiently flexible to transmit a substantial portion of pressureexerted against said second surface by transport gas present within saiddownstream chamber to said peripheral surface by said first surface whentransport gas is flowing through said transport gas flowpath.
 19. Theparticle blast system of claim 16, wherein said seal includes anupstream chamber, said at least one first opening being in fluidcommunication with said inlet through said upstream chamber.
 20. Theparticle blast system of claim 19, wherein a wall is defined by saidfirst surface and a second, spaced apart surface, said wall beingsufficiently flexible to transmit a substantial portion of pressureexerted against said second surface by transport gas present within saidupstream chamber to said peripheral surface by said first surface whentransport gas is flowing through said transport gas flowpath.
 21. Theparticle blast system of claim 16, wherein there is no substantial forcebetween said peripheral surface and said first surface when transportgas is not flowing through said transport gas flowpath.
 22. The particleblast system of claim 16, wherein said first surface is urged intosealing contact with said peripheral surface when transport gas isflowing through said transport gas flowpath.
 23. The particle blastsystem of claim 22, wherein substantially all sealing force between saidfirst surface and said peripheral surface is created by said transportgas flowing through said transport gas flowpath.
 24. The particle blastsystem of claim 16, wherein a wall is defined by said first surface anda second spaced apart surface, said wall being sufficiently flexible totransmit a substantial portion of pressure exerted against said secondsurface by transport gas to said peripheral surface by said firstsurface when transport gas is flowing through said transport gasflowpath.
 25. The particle blast system of claim 16, wherein saidtransport gas is able to flow from said at least one first opening tosaid at least one second opening only through those of said plurality ofpockets disposed between said first and second positions.
 26. Theparticle blast system of claim 16, wherein a portion of said transportgas does not flow through said first and second openings.
 27. Theparticle blast system of claim 16, comprising a passageway defined atleast partially by said seal, a portion of transport gas being able toflow from said at least one first opening to said at least one secondopening through said first passageway.
 28. The particle blast system ofclaim 16, wherein said plurality of pockets are arranged such that saidtransport gas is able to flow continuously from said at least one firstopening to said at least one second opening when said rotor is rotated.29. The particle blast system of claim 16, wherein said wall contactssaid peripheral surface over an angle of about 180°.
 30. The particleblast system of claim 16, wherein said seal is of unitary construction.31. A feeder configured to transport blast media from a source into atransport gas flow, said feeder assembly comprising: a) a rotor having aperipheral surface, said rotor being rotatable about an axis ofrotation; b) a plurality of pockets disposed in said peripheral surface,each of said plurality of pockets being cyclically disposed between afirst position and a second position when said rotor is rotated aboutsaid axis; and c) a transport gas flowpath, said transport gas flowpathhaving an inlet and an outlet, said inlet being configured to beconnected to a source of transport gas, said inlet being in fluidcommunication with said outlet through those of said plurality ofpockets disposed between said first and second positions.
 32. The feederof claim 31, wherein said inlet is in fluid communication with saidoutlet only through said those of said plurality of pockets disposedbetween said first and second positions.
 33. The feeder of claim 31,wherein said plurality of pockets are arranged such that said inlet isin continuous fluid communication with said outlet when said rotor isrotated.
 34. A method of delivering blast media to a discharge nozzle,comprising the steps of: a) providing a rotor configured to introducesaid blast media into a flow of pressurized transport gas, said rotorhaving a first rotor surface; b) providing a seal, said seal having afirst seal surface disposed adjacent said first rotor surface; c)starting rotation of said rotor prior to exerting any substantial forceby said first seal surface on said first rotor surface; d) afterrotation of said rotor has started, exerting force by said first sealsurface on said first rotor surface, forming a seal therebetweensufficient to prevent any substantial leakage of said pressurizedtransport gas across said formed seal.
 35. The method of claim 34,wherein said step of exerting force comprises the step of applying fluidpressure to said seal.
 36. The method of claim 35, wherein said fluidpressure is applied by said flow of pressurized transport gas.
 37. Themethod of claim 36, wherein said fluid pressure applied by said flow ofpressurized transport gas is applied by fluid disposed in a passageway,said passageway being in fluid communication with said flow of transportgas and with said seal.
 38. The method of claim 37, wherein said fluiddisposed in said passageway is pressurized transport gas.
 39. The methodof claim 37, wherein a significant portion of said pressurized transportgas does not flow through said passageway.
 40. The method of claim 36wherein said flow of pressurized transport gas is controlled by a valve,there being no substantial flow of pressurized transport gas when saidvalve is substantially closed, further comprising the step of openingsaid valve to initiate said flow of pressurized transport gas atapproximately the same time that rotation of said rotor is started. 41.The method of claim 36 wherein said flow of pressurized transport gas iscontrolled by a valve, there being no substantial flow of pressurizedtransport gas when said valve is substantially closed, furthercomprising the step of opening said valve at a time relative to saidstarting rotation of said rotor such that said rotor has startedrotating before any appreciable torque is produced on said rotor as aresult of said flow of pressurized transport gas.
 42. A seal configuredfor use in feeder of a particle blast system, said feeder having arotor, said rotor having a peripheral surface and at least one pocketformed in said peripheral surface, said rotor being rotatable about anaxis of rotation, said at least one pocket being cyclically disposedadjacent a first position when said rotor is rotated, said at least onepocket being configured to discharge blast media therefrom at said firstposition, said seal comprising: a) said first surface configured tocontact at least a portion of said peripheral surface, said firstsurface defining one surface of at least one wall, said wall includingat least one second surface spaced apart from said first surface; b) atleast one passageway configured for said blast media to flowtherethrough; c) at least one opening in said first surface, said atleast one passageway in fluid communication with said at least oneopening; and d) said wall being sufficient flexible to transmit asubstantial portion of fluid pressure exerted against said at least onesecond surface to said peripheral surface.
 43. The seal of claim 42,wherein said at least one passageway is defined at least partially bysaid at least one second surface.
 44. The seal of claim 42, wherein saidat least opening comprises a first and a second passageway, and said atleast one passageway comprises a first and second chamber, said firstpassageway being in fluid communication with said first opening and saidsecond passageway being in fluid communication with said second opening,and wherein said at least one second surface at least partially definessaid first and second passageways.
 45. The seal of claim 42, whereineach of said at least one wall is arcuate.
 46. A feeder configured totransport blast media from a source into a flow of transport gas, saidfeeder assembly comprising: a) a first opening and a second opening,said first and second opening being spaced apart from each other, eachopening having a respective inner diameter; b) a rotor having aperipheral surface, said rotor being rotatable about an axis ofrotation; c) a plurality of pockets disposed in said peripheral surface,each of said plurality of pockets being cyclically disposed at a firstlocation at which blast media is delivered thereinto, and a secondlocation at which at least a portion of said blast media is dischargedtherefrom; and d) said rotor having a first portion of said peripheralsurface, said first portion having a diameter configured to be receivedand supported by said inner diameter of said first opening, said rotorhaving a second portion of said peripheral surface, said second portionhaving a diameter configured to be received and support by said innerdiameter of said second opening, said diameter of said first portionbeing no larger than said inner diameter of said second opening, saidperipheral surface having a maximum diameter between said first portionand said second portion no greater than the inner diameter of saidsecond opening of said second portion whereby said rotor may beinstalled in said feeder by inserting said first portion first throughsaid second opening to a position at which said first portion isreceived and supported by said first opening, said second portion beingreceived and supported by said second opening at said position.
 47. Thefeeder of claim 46, wherein said first and second openings are definedby respective bearings.
 48. A feeder configured to transport blast mediafrom a source into a flow of transport gas, said feeder comprising: a) arotor having a peripheral surface, said rotor being rotatable about anaxis of rotation; b) a plurality of pockets disposed in said peripheralsurface, each of said plurality of pockets being cyclically disposedbetween a first position and a second position when said rotor isrotated about said axis; c) a transport gas flowpath, said transport gasflowpath having an inlet and an outlet, said inlet being configured tobe connected to a source of transport gas; d) a seal having a firstsurface contacting at least a portion of said peripheral surface, saidfirst surface having at least one first opening disposed adjacent saidperipheral surface, said seal defining a first passageway which is influid communication with said at least one first opening and with saidinlet, said seal defining a second passageway which is in fluidcommunication with said at least one first opening and said outlet, saidfirst passageway being in fluid communication with said secondpassageway at said at least one first opening.
 49. The feeder of claim48, further comprising a wall disposed between said first and secondpassageways, said wall having a first edge spaced from said peripheralsurface forming a gap between said wall and said peripheral surface, aportion of said flow of transport gas being able to flow through saidgap from said first passageway to said second passageway.
 50. A feederconfigured to transport blast media from a source into a flow oftransport gas, said feeder comprising: a) a rotor having a peripheralsurface, said rotor being rotatable about an axis of rotation; b) aplurality of pockets disposed in said peripheral surface, each of saidplurality of pockets being cyclically disposed between a charge positionat which blast media is introduced into said pockets and a dischargeposition at which blast media is discharged from said pockets; c) atransport gas flowpath, said transport gas flowpath having an inlet andan outlet, said inlet being configured to be connected to a source oftransport gas, a portion of said transport gas flowpath being disposedadjacent said discharge position such that blast media discharged fromsaid pockets is carried therefrom by the transport gas; d) a seal havinga first surface contacting at least a portion of said peripheral surfaceat said discharge position, said seal configured to seal against apressure of the transport gas of at least approximately 30 PSIG; and e)said rotor having a diameter no greater than approximately four inches.51. A feeder configured to transport blast media from a source into aflow of transport gas, said feeder comprising: a) a rotor having aperipheral surface, said rotor having a sealed width and a diameter,said rotor being rotatable about an axis of rotation; b) a plurality ofpockets disposed in said peripheral surface, each of said plurality ofpockets being cyclically disposed between a charge position at whichblast media is introduced into said pockets and a discharge position atwhich blast media is discharged from said pockets; c) a transport gasflowpath, said transport gas flowpath having an inlet and an outlet,said inlet being configured to be connected to a source of transportgas, a portion of said transport gas flowpath being disposed adjacentsaid discharge position such that blast media discharged from saidpockets is carried therefrom by the transport gas; d) a seal having afirst surface contacting at least a portion of said peripheral surfaceacross said sealed width at said discharge position,; and e) said rotorhaving a ratio of said diameter to said sealed width approximately nogreater than 1:2.
 52. The feeder of claim 51, wherein said ratio isapproximately 1:1.
 53. A feeder configured to transport blast media froma source into a flow of transport gas, said feeder comprising: a) arotor having a peripheral surface, said rotor being rotatable about anaxis of rotation; b) a plurality of pockets disposed in said peripheralsurface, each of said plurality of pockets being cyclically disposedbetween a charge position at which blast media is introduced into saidpockets and a discharge position at which blast media is discharged fromsaid pockets; c) a transport gas flowpath, said transport gas flowpathhaving an inlet and an outlet, said inlet being configured to beconnected to a source of transport gas, a portion of said transport gasflowpath being disposed adjacent said discharge position such that blastmedia discharged from said pockets is carried therefrom by the transportgas; d) a seal having a first surface contacting at least a portion ofsaid peripheral surface at said discharge; and e) said rotor having nosubstantial axial force being exerted thereon.
 54. A feeder configuredto transport cryogenic blast media from a source into a flow oftransport gas, said feeder comprising: a) a rotor having a peripheralsurface, said rotor being rotatable about an axis of rotation; b) asupport structure, said rotor being rotatably supported by said supportstructure; c) a plurality of pockets disposed in said peripheralsurface, each of said plurality of pockets being cyclically disposedbetween a charge position at which blast media is introduced into saidpockets and a discharge at which blast media is discharged from saidpockets; d) a transport gas flowpath, said transport gas flowpath havingan inlet and an outlet, said inlet being configured to be connected to asource of transport gas, a portion of said transport gas flowpath beingdisposed adjacent said discharge position such that blast mediadischarged from said pockets is carried therefrom by the transport gas;e) a seal having a first surface contacting at least a portion of saidperipheral surface at said discharge position; and f) substantially allheat gain to or heat loss from said rotor is from contact between theblast media and said rotor and from said transport gas flowing throughsaid pockets.
 55. A method of delivering blast media to a dischargenozzle, comprising the steps of: a) providing a rotor configured tointroduce said blast media into a flow of pressurized transport gas at adischarge station, said rotor having a first rotor surface, said rotorhaving a diameter no greater than approximately four inches; b)providing a flow of transport gas having a pressure of at leastapproximately 30 PSIG; and c) sealing between said first rotor surfaceand said discharge station sufficient to prevent any substantial leakageof said pressurized transport gas.